Scanning system



Jan. 14, 1947. v M O 2,414,096

SCANNING SYSTEM Filed Feb. 4, 1944 R. F AMPLIFIER MOOUL A TOR ATTOR EVPatented Jan. 14, 1947 Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application February 4, 1944,Serial No. 521,106

12 Claims.

This invention relates primarily to scanning systems and moreparticularly to oscilloscopic systems providing a definite time orreference axis along which scanned information of one character oranother may be displayed.

An illustrative system of the kind described is a so-called panoramicradio receiving system comprising electrical scanning means forcontinuously traversing a predetermined radio frequency range and acathode-ray oscilloscope for indicating simultaneously at preassignedrespective points along a reference axis the frequencies at which radioactivity is encountered. The reference axis may be in the form, forexample, of a single line that is continuously scaled, in terms offrequency, from one-end to the other. The presence of radio activity atany particular frequency may be indicated by a luminous spot or spikethat is made to appear at the corresponding point alon the frequencyscale.

An object of the invention is to provide an im proved oscilloscopicsystem in which the reference axis along which information is displayedcomprises a multiplicity of separated portions. A more particular objectis to insure that all of the collected information is displayednotwithstanding the finite time required for the cathode ray or the liketo pass from the end of one portion of the reference axis to thebeginning of another.

In a panoramic receiver embodying the present invention the frequencyscale takes the form of a multiplicity of parallel lines on the screenof a cathode-ray oscilloscope. These lines are traversed in successionby the cathode ray while the frequency scanner once traverses thefrequency range of interest. The operation of the frequency scanner isso controlled that its progression across the frequency range iseifectively halted during :hose intervals in the scanning cycle when the:at-hode ray is passing from one of the scale por- ;ions to another.

The nature of the present invention will appear nore fully from aconsideration of the embodinent illustrated in the accompanying drawing,in vhich:

Fig. 1 illustrates a panoramic receiver in ac- :ordance with theinvention; and

Figs. 2, 3 and 4 are diagrams illustrating the vperation of certain ofits components.

Referring more particularly now to Fig. 1, the vanoramic receivingsystem shown schematically herein comprises a radio receiving antenna land radio frequency amplifier 2 through which all f the received waveslying within a predetermined frequency range are applied to themodulator 4 is cyclically varied, in a manner to be described, betweenlimits such that at the output of modulator 3 one of the sidebandsderived from the appliedradio frequency range is swept repeatedly, fromone extremity to the other, across the pass frequency of filter 5. Thepass band of filter 5- is made narrow enough to selectively transmit insuccession all of the radio signals that may appear in the applied band.In effect, the frequency scanner repeatedly traverses the applied radiofrequency range and during each traverse transmits momentarily and insuccession the various radio signals that are encountered. Theinformation collected by the frequency scanner is delivered at theoutput of filter 5 in the form of a succession of wave effects or wavepulses, and these are delivered through amplifier 6 to the control gridI i of a cathode-ray tube I0.

Cathode-ray tube ID comprises control grid II for controlling theintensity of the cathode ray. a luminescent screen l2 for the display ofthe collected information, means I 3 for deflecting the cathode ray inthe horizontal plane-and means I 4 for deflecting the ray in thevertical plane. The two deflectin means are shown as two pairs ofdeflecting plates although they could as well be two sets of magneticdeflecting coils. The cathode-ray tube In may be so biased, by means notshown, that the luminous spot or trace which the cathode ray tends toproduce on screen I2 is just barely extinguished except when signaleffects are applied to the control grid 1 l.

Deflecting plates M are connected to a sweep circuit 20 which applies tothem a saw-toothed voltage wave as illustrated at A in Fig. 3. Thiscauses the point of impingement of the cathode ray on screen I 2 to moveperiodically in a vertical direction across screen I2 at a periodic ratefixed by the operating frequency of the saw-toothed wave source 20. Thelatter is the same as the repetitive rate of frequency scanning and maybe, for example, 15 cycles per second. The shape of the saw-toothed waveA is such that the spot or point of impingement of the cathode ray movesrelatively slowly from, say, top to bottom of screen l2 while thevoltage A is rising, and returns relatively quickly while the voltage Ais falling. During the latter period, the flyback or retrace period, thecathode ray may be suppressed in 3 known manner to prevent any markbeing made on the screen.

Sweep circuit as produces a saw-toothed voltage wave B that is of thesame shape as voltage wave A but its frequency is a multiple thereof. Itmay be assumed by way of example that the frequency of the one is eighttimes that of the other, as illustrated in Fig. 3, and that this harmonic relation is maintained by any suitable synchronizing means. Theoutput of sweep circuit 39 is applied through amplifying pentode 3i andamplifier 32 to deflecting plates l3 whereby the cathode ray isdeflected horizontally across the screen l2 at a rate of 120 cycles persecond. The bias and polarity may be assumed to be such that during eachsecond the spot moves relatively slowly from right to left across thescreen and returns relatively quickly during the flyback periodpertaining to wave B. Disregarding the fact that the cathode ray or spotmay be extinguished much of the time, the path traced on the screen 12by the cathode ray as a result of the two components of displacementimparted to it is of the form illustrated in Fig. 2. It will beunderstood that this path is cyclically traversed fifteentimes a second.The relatively slow movements of'the spot are indicated by the solidlines in Fig. 12 while the relatively rapid flyloack movements arerepresented by dotted lines.

Although the reference axisrepresented by the multiplicity of solidlines is discontinuous, it is an object Of the invention to arrange thatthese separate lines or scale portions shall together pro vide acontinuous frequency scale embracing all of the radio frequencies withinthe range traversed by the frequency scanner. In other words, it isdesired that if the left-hand end of one line represents a certain radiofrequency the righthand end of the next line shall represent the nextadjacent frequency, or that there shall be an overlap rather than anhiatus. One of the difficulties to be overcome in this connection isthat while the cathode ray is moving from left to right during theinterline fiyback periods the frequency scanner would ordinarilycontinue its traverse across the radio frequency range during theseperiods, with the result that signals encountered in certain portions ofthe scanning cycle would be lost in so far as their indication on thefrequency scale is concerned.

As indicated hereinbefore the present invention provides for effectivelyhalting or suspending the progressive scanning operation during theinterline flyback periods so that no radio frequencies are passed overby virtue of the scanner continuing to advance across the frequencyrange while the cathode ray is passing from the end of one scale portionto the beginning of the next. It is not essential that the scanner becompletely stopped but rather that there be no net progression of thescanner during the interline flyback periods. In the Fig. '1 system thescanning operation is reversed rapidly at the beginning of each fiybackperiod and immediately allowed to resume so that by the end of thefiyback period the scanner has again reached, or at least not passedbeyond, the frequency that it had reached before reversal ofthedirection of scanning. The circuit means provided for this operation areas follows.

The saw-toothed voltage wave A produced by sweep circuit 22' is appliedto a control'grid of the amplifying space discharge device 2| which maybe of the pentagrid mixer type, and after further amplification inam'plifier'ZZ it is applied with the proper polarity to avoltage-responsive frequency controlling portion of beating oscillator4. Oscillators of the character described are well known in the art andit suffices to say that the applied voltage wave A varies the operatingfrequency between the necessary limits. The polarity may be such, forexample, that during each cycle of the voltage Wave A the operatingfrequency tends to increase relatively gradually from a lower extremevalue to an upper extreme value and then to fall rapidly to the initialvalue during the flyback period associated with wave A. The frequencyscanner tends to scan the applied radio frequency range in the samemanner at the assumed rate of fifteen times per second, which is theperiodic rate at which the cathode ray traverses the path described withreference to Fig. 2.

Saw-toothed voltage wave B, regulated to the proper amplitude andillustrated in exaggerated form at C in Fig. 3, is applied concurrentlywith voltage wave A to control the operating frequency of oscillator A.This added component is, or may be, derived from sweep circuit 36 by wayof a potential divider 33 that is interposed in the common grid-anodecircuit of pentode 3|, the potential divider being connected in turn toanother control grid in the amplifying space discharge device ii. Theresultant wave applied to oscillator t is illustrated at A+C in Fig. 3with the serrations exaggerated to show more clearly the character ofthe wave shape.

The latter illustration will serve to illustrate also the variations inthe frequency of oscillator and the progression of the frequency scanneracross the applied radio frequency range. Thus at the beginning of acycle while the cathode ray traverses the uppermost scale portion thefrequency scanner traverses progressively the corresponding portion ofthe radio frequency range. At the beginning of the interline flybackperiod the scanner is quickly set back a certain amount and-then resumesits relatively gradual progression in the initial direction acros thefrequency range. The amplitude of voltage wave 0 is so adjusted by meansof potential divider 33 that by the end of the interline flyback periodthe scanner has again just reached the radio frequency that was reachedat the beginning of the fiyoackperiod, so that the beginning of thesecond scale portion coincides with the end of the first scale portionand the two taken in succession afford a continuous frequency scale. Thescanner continues its progression while the cathode ray traverses thesecond scale portion, until the beginofthe next flyback period isreached and the scanner is again momentarily set back or temporarilyreversed. This process is repeated until in sli htly less thanone-fifteenth second all of the scale portions have been traversed insuccession and the flyback associated with Voltage wave A begins. Duringthe latter flyback period the spot returns to the beginning of the firstscale portion and the scanner returns to its initial-position in theradio frequency spectrum.

It will be understood that whenever the scanner encounters radioactivity in its progression across the frequency range'the cathode rayproduces a luminous spot at the corresponding frequency position on thescreen'lt. It will be understood too that the visual indicationrepresenting a particular radio transmitter may be split, part appearingat the'left-hand extremity of one scale portion and part at theright-hand extremity of the next scale portion. If a certain overlap beallowed as suggested hereinbefore, stations represented at or near theleft-hand end of one scale portion will be duplicated at or near theright-hand end of the next, but none will be omitted. In the lattercase, one or the other of the duplicate scale portions may bedisregarded or covered over if desired. A few of thetransmission-indicating spots are shown in Fig. 1. Although the screenI2 may have a frequency scale inscribed on it along the scale portionsillustrated in Fig. 2, such a scale may instead be inscribed on aremovable transparency, or electrical auxiliaries known in the art maybe employed for indicating or determining the radio frequencyrepresented by any particular luminous spot. In any case, the severalscale portions collectively cover the entire radio frequency range ofinterest.

Whereas the several scale portions are inclined as illustrated in Fig.2, they may be made horizontal if desired. by applying to the deflectingplates M a saw-toothed voltage wave having the shape illustrated at D inFig. 4. .Ehis wave may be derived from sweep circuit 30, through aswitch connected to the output circuit of pentode 3!, a indicated inFig. 1. The amplitude of the vave D is such that combined with thesawtoothed voltage wave A it produces a horizontally stepped Voltagewave A-l-D as shown in Fig. 4. The net result is that the somewhattrapezoidal portion of Fig. 2 becomes strictly rectangular. In otherrespects the operation of the system is as hereinbefore described.

Although the present invention has been described largely with referenceto a specific embodiment it will be understood that the invention may beembodied in various other forms within the spirit and scope of theappended claims.

What is .claimed is:

1. An oscilloscopic system comprising, in combination, selective meansfor cyclically scanning a predetermined subject and selecting insuccession in the course of each cycle effects appearing at variouspoints therein, oscilloscopic means for marking the selected effect-sindividually along a multiplicity of separated reference linesconstituting an extended time base, said oscilloscopic means includingmeans for driving said marking means along said reference lines incyclically repeated succession, and means for interrupting the saidscanning during the periods within each scanning cycle during which saidmarking means passes from one of said lines to another of said linesrepresenting a subsequent portion of said extended time base.

2. In combination, selective means for cyclically scanning apredetermined subject and selecting in succession effects appearing atdifferent points therein, oscilloscopic means for cyclically traversinga predetermined path and visually indicating the selected effects atrespectively corresponding points along said path, said path comprisinga multiplicity of separated portions along which all of the selectedeifects are to be indicated, and canning control means for preventingany net progression of said selective means relative to said subject inthe period-s during which the path between said separated path portionsis being traversed.

3. In combination, selective means for cyclically scanning apredetermined subject and selecting in succession effects appearing atdifferent points therein, oscilloscopic means for cyclically traversinga predetermined path and visually indicating the selected effects atrespec tively corresponding points along said path, said pathcomprising, a multiplicity of separated por tions along which all oftheselected effects are to be indicated, and scanning control means forpreventing any net progression of'said selective means through saidsubject in the periods during which the path between said separated pathportions is being traversed, said scanning control means comprisingmeans for temporarily reversing the direction of progression of saidselective 'means through said subject within the said periods.

4. In combination, cathode-ray oscilloscopic means, sweep circuit meansadapted to drive the cathode ray cyclically along a predetermined pathcomprising a multiplicity of disconnected path portions, frequencyscanning means for cyclically scanning a predetermined wave frequencyrange and selecting in succession wave effects of differ?- entfrequencies appearing in said range, said scanning means having acyclical rate such that it progresses once across said frequency rangewhile said cathode ray covers said multiplicity of path portions, meansoperative on said scanning means for preventing any net progression ofthe said scanning means across said frequency range in the period withineach scanning cycle during which the cathode ray passes from one of saidpath portions to the next, and means for varying said cathode ray underthe control of the wave effects selected by said scanning means.

5. In combination, frequency translating means having wave inputmeansfor the simultaneous application of any waves lying within apredetermined frequency range and wave output means, voltage-responsivemeans for varying the extent of translation effected by said frequencytrans.- lating means, means for applying to said responsive means aperiodically varying voltage which throughout a substantial part of eachperiod of its variation changes substantially continuously andprogressively in the same sense of change with relatively briefintermittent changes in the opposite sense, means for visuallyindicating the waves present in said range comprising an oscilloscopeand frequency selective means connecting said oscilloscope and said waveoutput means.

6. In combination, selective means for cyclically scanning apredetermined subject and during each cycle selecting in successioneffects appearing at discrete points therein, voltageresponsive meansfor controlling the progression of said scanning means through saidsubject, means for effectively halting the said progression of saidscanning means repeatedly during each cycle comprising means forapplying a periodic voltage wave to said voltage-responsive means, acathode-ray tube, cathode-ray directing means adapted to drive thecathode ray around a predetermined path periodically in isochronism withthe cyclical scanning, and ray controlling means responsive to theeffects successively selected by said scanning means.

7. In combination, selective means for scanning a predetermined subjectand selecting in succession efiects that may appear at various pointstherein, voltage-responsive means for controlling the progression ofsaid scanning means through said subject, a cathode-ray tube comprisingtwo deflecting means for variably deflecting the cathode ray inrespectively different directions, means for applying a periodicsubstantially saw-toothed wave to one of said deflecting means, meansfor applying to the other of said deflecting means a periodicsubstantially sawtoothed wave that is harmonically related to thefirst-mentioned wave, means for applying both of said waves to saidvoltage-responsive means with such relative polarity that theprogression of said scanning means during the period of saidfirst-mentioned 'wave is momentarily interrupted at the periodic rate ofthe second-mentioned wave, and means for representing all of the saideffects at respective .points along said path comprising cathode-rayvcontrolling means actuated by the selected effects.

said oscillator a periodic control voltage which throughout a pluralityof separated parts of its .period changes in value in the samedirection, the initial value ineach said part except the first beingsubstantially equal to the final value in the next preceding part andthe interval separating said parts being small in comparison with thelengths thereof, filter means connected to the output of said modulatorfor selecting the received signals in periodically repeated succession,a cathode ray tube, ray deflecting means for driving the cathoderayalonga multiplicity of separated path portions in succession in such timedrelation with the change in said periodic Voltage that the ray passesfrom the end of one path portion to the beginning of the nextsubstantially wholly withinthe'interval separating respectivelycorresponding parts of the control voltage period, and ray controllingmeans responsive to the signals selected by said filter means forseparately indicating the several signal-s along said path portions.

9. A panoramic receiver in accordance with claim 8 in which the saidintervals separating said parts of the control voltage period are atleast several in number.

10. A panoramic receiver in accordance with claim 8 in which said meansfor supplying said periodic control voltage comprises a, periodicsawtoothed voltage wave generator and means synchronized therewith forgenerating a periodic voltage wave the frequency of which is a multipleof the frequency of said saw toothed voltage wave.

11. A panoramic receiver in accordance with claim 8 in which said meansfor supplying said periodic control voltage comprises two sawtoothedvoltage wave generators the frequencies of which are harmonicallyrelated, and in which said raydefiecting means includes means fordeflecting the ray under the joint control of the two saw-toothedvoltage waves.

12. A panoramic receiver in accordance with claim 8 comprising means forgenerating two harmonically related saw-toothed voltage waves one ofwhich has a frequency at least several times that of the other, meansfor combining said two waves to form a resultant saw-toothed wave havinga flank that slopes substantially continuously in one direction withperiodically repeated excursionsthat are opposite in direction of slopeand of relatively small extent and duration, said resultant constitutingsaid periodic control voltage, said ray deflecting means including tworay deflectors for deflecting the ray in respective mutuallyperpendicular planes, and means for applying each of said harmonicallyrelated waves to a respective one of said deflectors.

THOMAS L. 'DIMOND.

